A method and a corresponding device of this type are described in U.S. Pat. No. 4,745,469, where an axis measurement is performed on the basis of the ascertained axis of rotation, in particular the trail angle and the camber angle are ascertained, while the vehicle is on a chassis dynamometer. Using a projection system, laser lines or other patterns are projected onto the wheel or onto the tire. Using cameras, the patterns are imaged and the 3D coordinates are reconstructed on the surface from the camera coordinates and from the conventional arrangement of the cameras with respect to the projector via triangulation, and the position of the wheel is ascertained therefrom, from which finally the trail (angle) and the camber (angle) are determined. This contactless optical measurement takes place while the wheel rotates about its axis of rotation, fixedly mounted in the chassis dynamometer.
German Patent Application No. DE 103 35 829 A1 also describes a method for determining the axis geometry in which a light pattern is projected onto the front of the wheel and the light reflected from the front of the wheel is recorded by an image converter from a direction different from the projection direction, a flat projection of the light and a flat recording of the light reflected by the wheel during the rotation of the wheel being provided to determine the normal vector of the wheel or a reference plane as accurately and robustly as possible despite the unevenness present on typical wheels. The reference plane and the related normal vector are ascertained on a rotating wheel which executes at least one complete revolution. A strip pattern, a monochrome grid structure, or a two-dimensional color pattern are preferably used as projected light patterns.
German Patent Application No. DE 10 2005 063 082 A1 and DE 10 2005 063 083 A1 also describe methods for optical chassis measurement in which structured light is projected onto the wheel and also onto the surrounding body areas and is recorded using an imaging sensor system.
In other methods and devices for ascertaining the axis of rotation and measuring the axis geometry, the vehicle wheel is observed using a mono or stereo camera system such as described, for example, in European Patent No. EP 0 895 056 A2 and German Patent Application No. DE 29 48 573 A1. Distinctive features such as, for example, the rim edge, are located in the grayscale image of the camera display. From the geometric position of the rim edge or other features in the image, their spatial position and, from there, their trail and camber, are calculated. A measuring method of this type is also performed in German Patent Application No. DE 10 2004 013 441 A1, where a 3D model is fitted for ascertaining the axis of rotation of the wheel. During the measurement, stereo pictures of the wheel rim are also taken and the angular position of the valve is established. German Patent Application No. DE 10 2005 017 624.0 describes obtaining wheel features and/or body features by ascertaining a 3D point cloud to determine the wheel geometry and/or the axis geometry of vehicles therefrom, the rotating wheel being recorded, in particular, also while the vehicle is passing by.
There are also methods in which instead of existing wheel features, special markings are applied using a mechanical arrangement such as described, for example, in German Patent Application No. DE 100 32 356 A1. While markings of this type provide structures on the wheel that are easily detectable for measuring and analysis, they require additional effort.
In contrast, in previous methods and devices without special markings or using projected light, it is difficult to obtain exact and reliable, robust measurements of the axis geometry or wheel geometry and of the axis of rotation of a vehicle wheel, in particular under the rough measuring conditions of a workshop testing site and complying with the requirement of the simplest possible performance of the measurement.